Asymmetric Cu Valence Engineering in CuInS2 Enables Selective Photocatalytic CO2-to-C2H4 Conversion

Abstract Achieving efficient C–C coupling in photocatalytic CO2 reduction is fundamentally limited by the inability of semiconductor surfaces to simultaneously stabilize and differentiate key intermediates (*CO and *CHO). In this work, we establish an asymmetric Cu valence engineering strategy in tetragonal CuInS2 that enables continuous tuning of the Cu+/Cu2+ ratio without altering the crystal framework. It is revealed that the Cu valence distribution is closely correlated with C2H4 selectivity, while the morphology, surface area, sulfur vacancy, and interfacial environment collectively contribute to the overall photocatalytic activity. Operando spectroscopy and DFT calculations show that such Cu valence-asymmetric sites create a polarized adsorption for key intermediates, where Cu+ preferentially stabilizes *CO and Cu2+ lowers the barrier for *CHO formation, promoting cooperative C–C coupling via the *OC–CHO intermediate. As a result, the optimized CuInS2-1.5SC achieves an ethylene production rate of 73.9 ± 6.3 μmol g–1 h–1 with 95.4 ± 1.0% product selectivity and 98.0 ± 0.6% electron selectivity, without any cocatalysts or sacrificial agents. This work demonstrates the Cu valence distribution as an important parameter for regulating C2H4 selectivity and highlights the cooperative contribution of electronic, structural, and interfacial factors to efficient photocatalytic CO2-to-C2H4 conversion.